1. Field of the Invention
This invention relates to electric immersion heaters.
2. Description of the Related Art
Electric immersion heaters are very widely used in water heating electric appliances such as kettles, hot water jugs, washing machines, dish washers, urns etc. The standard form of immersion heater comprises an elongate metal sheathed element which is formed into a tortuous configuration to provide the required length of element within the size constraints of the water heating vessel. It is traditional that the element terminates in so-called cold leads by means of which electric connections are made to the heater. There is also generally provided an intermediate "hot return" portion which in use is in thermal contact with a thermally sensitive actuator of a control device which incorporates a switch for disabling the heater in the event of it overheating in consequence of there being insufficient water in the vessel to cover the element.
Such immersion heaters are used as standard in most electric kettles and hot water jugs. They are traditionally located in the lower part of such a vessel so that a minimum amount of water can be boiled. Since an immersion heater is substantially surrounded by water, heat generated from all sides of the heating element is dissipated which renders an immersion heater more efficient than heaters which are mounted externally of the water containing vessel and which heat the water via a vessel wall. This latter form of heater is less efficient in that heat dissipated from the side of the heating element remote from the vessel wall is essentially wasted. Such heaters are generally run at a higher temperature than immersion heaters and therefore more prone to failure.
Known immersion heaters do have certain drawbacks. In particular, they are, to an extent, aesthetically unpleasing. This is particularly so when they become covered in scale as is inevitable in the longer term. The shape of known heating elements makes them difficult to clean, and it is also difficult to clean the base of the vessel even though this remains visible through the heater. Whilst in the UK and other countries users of electric kettles and hot water jugs have to a degree accepted the unpleasing appearance of the lower region of the vessel interior, in some countries there is a strong reluctance for this reason to use immersion heaters and it is still more common to find the less efficient externally mounted heaters discussed above.